The present invention relates to a piston head and the method for manufacturing particularly an articulated, or two-piece, piston head provided with a closed cooling chamber on its top portion.
Closed cooling chambers of pistons of the prior art, including articulated pistons, can be made by the gravity casting method only. However, this method has proven to be inadequate for making articulated piston heads since the product may lack the structural strength required to withstand the high thermal and mechanical loads imposed to the piston head top portion during the combustion process.
In the known articulated pistons the cooling chamber is of the so-called semi-open type, which is defined by a groove on the underside of the top and a tray provided on the skirt upper portion. In such cooling chambers, the cooling medium is supplied to the chamber by a nozzle, located at the engine crank-case, and circulates in the chamber. Due to the reciprocating motion of the piston the cooling medium splashes against the combustion bowl lower wall and the ring zone inner wall, thereby removing part of the heat generated in said regions.
However, for certain applications it is desirable to maintain the cooling medium for a longer period of time inside the cooling chamber, which not only increases the efficiency of the cooling process but also makes possible using substantially smaller quantities of cooling medium (engine lubricating oil), thus requiring an oil pump with a lower output.